1. Field of the Invention
The present invention relates to a zoom lens system and an image pickup apparatus including the zoom lens system. The present invention is suitable for use in, for example, a photographic camera, a video camera, an electronic still camera, a digital camera, and a 3-CCD electronic camera.
2. Related Background Art
When vibrations are incidentally transmitted to a photographing system, a photography image blurs. Conventionally, various zoom lens systems including a mechanism for making compensation for image blur caused by the accidental vibrations (image stabilizing mechanism) have been proposed. For example, there has been known an optical system in which a part of lens units composing the optical system is moved in a direction substantially perpendicular to the optical axis to make compensation for image blur caused by vibrations (Japanese Patent Application Laid-Open No. H07-128619, Japanese Patent Application Laid-Open No. H07-199124 (corresponding to U.S. Pat. No. 5,585,966), Japanese Patent Application Laid-Open No. 2001-066500 (corresponding to U.S. Pat. No. 6,414,800), Japanese Patent Laid-Open No. H06-337374 (corresponding to U.S. Pat. No. 5,652,678), and Japanese Patent Laid-Open No. H02-093620 (corresponding to U.S. Pat. No. 5,000,549).
In general, an optical system in which a lens unit (correction lens unit) which is a part of the photographing system is decentered in parallel in a direction perpendicular to the optical axis to correct image blur has an advantage that the image blur can be relatively easily corrected.
However, the optical system requires a drive means (actuator) for displacing the correction lens unit. Therefore, there is a problem in that the amount of produced decentering aberration increases at the time of image stabilizing.
For example, when the number of lenses composing the correction lens unit is large and thus the weight of the correction lens unit becomes higher, electrical driving requires large torque.
When an imaging magnification of the correction lens unit, refractive power thereof, and the like are not suitably set, a movement amount of the correction lens unit which is required to obtain a correction effect for a predetermined amount of image blur becomes large, with the result that a size of the entire optical system increases.
Therefore, in order to prevent optical performance from deteriorating at the time of correcting the image blur and to obtain a preferable correction characteristic, it is necessary that an optical arrangement of the correction lens unit be suitably set for the optical system including the image stabilizing mechanism.